1. Field of the Invention
The present invention relates generally to an excavating device using a jet liquid to break up and mix with the ground such that the mixture can be discharged.
2. Discussion of the Background
EP-A-0 890 708 describes an excavating device which has a plurality of jet excavating units adjoining one another. In the jet excavating unit a rotating jet device is provided which sprays high-pressure jet liquid onto the ground which is to be excavated, which as a result is broken down. While the jet excavating device is being pulled through the ground in the excavation direction, the channel behind the jet excavating unit, which is formed by the jet device, is filled with a hardenable material. In this way, a wall is formed in the ground. Any desired shape can be selected for the channel to be formed in the ground, by arranging a number of jet excavating units in a desired way with respect to one another.
The known excavating device provides considerable drawbacks in relation to the way in which the excavation is controlled. Because of the increase in earth pressure as the depth in the ground increases, the known excavating device, given a relatively homogeneous soil composition, tends to tilt forwards, since in an excavating device of this nature which extends over a depth, the lower part will be subject to a greater resistance from the soil to be excavated than the part being above it. Consequently, the displacement of the lower part tends to lag behind the displacement of the upper part.
The rotating jet device has the drawback of including a plurality of moving parts, for example a motor and bearings, which are susceptible to faults and wear. Moreover, while the wall is being formed, the jet excavating device is not accessible for maintenance or repair purposes. Consequently, the excavating device is unreliable. Another complication is that under natural conditions the soil composition almost always varies in the excavation direction and/or over the cross section of the channel to be excavated, in particular when excavating under a slope, where it is highly probable that it will be necessary to cut through various soil strata. The jet devices of one or various jet excavating units are then simultaneously cutting through different types of soil, for example clay and sand, which exhibit different cohesion properties and thus break down under different jetting conditions. The variations in the nature of the soil cannot be predicted accurately, not even if an extensive and detailed soil analysis is carried out. The resistance to which the plurality of mutually adjacent jet excavating units are exposed by different types of soil during excavation varies, for example as a result of a first jet excavating unit excavating the soil to be excavated in front of it more quickly and more easily than a second jet excavating unit of the same excavating device. Consequently, the first jet excavating unit may excavate too much soil, with the result that the stability of the excavation front is jeopardized. Moreover, settlement occurs, leading to subsidence at ground level.
Another drawback of the known excavating device with a plurality of mutually adjacent jet excavating units is that obstacles which are encountered during excavation (for example unexploded bombs or rocky objects which cannot be cut up) are difficult to remove. It is usually impossible to move the obstacle out of the path of the channel which is to be excavated, and consequently the excavation process has to be interrupted and the obstacle has to be dug out of the path of the channel to be excavated from ground level, since the excavation front in front of the excavating device is not accessible in any other way. This is time-consuming and expensive and also causes problems for the environment above ground level. In the particular case in which the obstacle is displaced out of the path of the channel to be excavated, this may entail high local forces which cause damage to the excavating device.
The present invention provides an excavating device which to a large extent eliminates the drawbacks outlined above.
Accordingly, the present invention advantageously provides an excavating device for forming a channel of predetermined cross section in the ground, in an excavation direction, comprising an assembly of jet excavating units, which together define the cross section of the channel and are each provided with at least one jet device which can be operated with jet liquid. The jet liquid, such as water, which flows out of the jet devices is directed at the relatively soft ground which is to be excavated and includes, for example, of clay, sand or peat or a combination thereof. As a result, the ground is broken up and mixed with the jet liquid, after which the mixture obtained can be discharged. The excavating device has at least one sensor which is connected to at least one of the jet excavating units, for measuring a force which is exerted on the at least one jet excavating unit by the ground substantially parallel to the excavation direction, and control means for controlling the excavation by the excavating device on the basis of the force measured by the at least one sensor.
The excavating device according to the invention has the advantage that the force from the jet excavating unit is transmitted to the particles of soil in part via water pressure and in part mechanically, rendering the use of an excavating liquid superfluous. This saves on costs for the liquid and facilities required therefor and also provides excavated soil which can be reused more easily.
Another advantage of the invention is that the excavation process carried out by a system of jet excavating units can be successfully managed and better control of the excavating device can be obtained. The excavation carried out by the individual jet excavating units can be activated separately on the basis of forces measured locally in the cross section of the channel, with the result that the excavating device can move along a desired path accurately and under control, for example in order to ensure that the assembly of jet excavating units run simultaneously.
It is also possible, in the event of variations in the nature of the soil which are already known, for example from soil analysis, for the level of force to be locally adjusted according to a specific nature of the soil.
Moreover, with the excavating device according to the invention there is no need to carry out the measurements of the flow rate and the concentration of the soil mixture to be discharged by each excavating unit, since a force measurement is carried out instead of having to keep up to date with the soil balance. The fact that it is no longer necessary to measure the concentration of the soil mixture in particular yields considerable economic and safety benefits.
Since the excavation by the jet devices of the excavating device according to the invention is adapted on a local basis, i.e. for each jet excavating unit or for each jet device, to the desired or possible advancement, the use of energy and jet liquid is minimized, resulting in economic and environmental advantages.
In a preferred embodiment of the excavating device according to the invention, the control means are adapted to set a flow rate of the jet liquid used in at least one of the jet devices. In this way, it is easy to set the excavation by the jet device. Preferably, the flow rate of the at least one jet device of the jet excavating unit connected to the at least one sensor is set. This makes the control means simple to implement, since there is no need to take into account the possibility of different jet excavating units influencing one another. Preferably, the control means are adapted to increase or reduce the flow rate of the jet liquid of the at least one jet device in the event of an increase or decrease, respectively, in the force measured by the at least one sensor. This has the advantage that the resistance which the excavating device is subject to from the soil during excavation can be kept within a permitted range. Preferably, the setting of the flow rate of the jet liquid of the at least one jet device can be varied, for example can be varied continuously or in steps, between a predetermined minimum level and a predetermined maximum level. As a result, it is possible for the resistance which the excavating device is subject to during excavation to be continuously adapted, so that the original horizontal stresses in the soil are affected as little as possible, and settlement leading to subsidence at ground level is prevented. To set the desired horizontal soil stresses, the control means are preferably adapted to vary, for example continuously or in steps, the flow rate of the jet liquid of the at least one jet device of at least one jet excavating unit between a predetermined minimum and a predetermined maximum level on the basis of the force measured by the at least one sensor connected to the at least one jet excavating unit.
In a preferred embodiment of the excavating device according to the invention, the control means are adapted to supply jet liquid to the at least one jet device of at least one of the jet excavating units where the force exceeds a defined level, and to restrict the supply of jet liquid to a minimum value when the force drops below said level. The control means determine the forces at the excavation front which occur at the location of the respective jet excavating units and use the relevant data to select the jet excavating unit or units where the force exceeds a defined level or the jet excavating unit where the force is highest. Then, only the one or more selected jet excavating units are provided with jet liquid as required, within defined limits, and the other jet excavating units are provided with only little or no jet liquid. At the one or more selected jet excavating units, a method of this nature will lead to the force falling to below a predetermined level over the course of time. The supply of jet liquid to the one or more selected jet excavating units is then minimized or interrupted altogether. Then, the control means once again select the jet excavating unit or units where the force exceeds a defined level at that moment or the jet excavating unit where the force is highest at that moment, and only the selected one or more jet excavating units are supplied with jet liquid, and so on.
In this way, the jet liquid is guided substantially to the one or more jet excavating units where it is most required, and no more jet liquid is supplied for any longer than is necessary on the basis of the measured force. In this way, the energy required for jet excavation is reduced to a minimum and is adapted to the prevailing soil conditions. If the total amount of jet liquid required for the excavating device exceeds the maximum capacity of the jet liquid supply system, the control means ensure that the velocity of the excavating device in the excavation direction is reduced, with the result that the amount of jet liquid required is reduced. If the total amount of jet liquid required is less than the maximum capacity of the jet liquid supply system, the velocity of the excavating device can be increased until the amount of jet liquid required is substantially equal to the maximum capacity of the jet liquid supply system.
In a preferred embodiment, the jet devices are each fed, via a line in which a controllable valve is incorporated, from a jet pump which supplies a constant flow rate of jet liquid, the fraction of the jet liquid flow which is not taken up by the jet devices being supplied, via at least one system line in which a controllable valve is incorporated, to a space of the jet excavating units. In this way, the total flow of jet liquid which is supplied to the excavating device is not influenced by the amount of jet liquid being used by the one or more jet excavating units at any given moment. The flow of jet liquid/soil mixture to be discharged is also constant. If the nature of the soil is such that the maximum capacity of the jet liquid supply system is required for one or more jet excavating units, the entire flow of jet liquid generated by the jet pump passes to the one or more jet excavating units, and there is no jet liquid flowing through the system line. In the other extreme case, in which none of the jet excavating units need any jet liquid, all the flow generated by the jet pump passes via the system line to a space of the jet excavating units.
Preferably, the control means are adapted to set the controllable valve in the at least one system line in such a manner that a delivery pressure set for the jet pump is marginally higher than the maximum pressure required for the jet devices. Due to the system pressure which can be varied in this way, the delivery pressure of the jet pump is not (much) higher than is strictly necessary, leading to a minimum pressure drop (and therefore a low energy consumption) across the controllable valves in the lines leading to the jet excavating units.
In a further preferred embodiment, the excavating device comprises a drive device for displacing the excavating device substantially in the excavation direction, which drive device is preferably controlled by the control means. This results in the advantage that the propulsive force and the speed at which excavation is carried out can be adapted to the total resistance which the excavating device is subject to during excavation of the soil to be excavated.
Preferably, the control means are adapted to measure the current amount of jet liquid required for the assembly of jet excavating units and to adapt the velocity of the drive device to the available flow of jet liquid for the assembly of jet excavating units.
In a further preferred embodiment the excavating device comprises a support structure which supports the jet excavating units, thus making the measurement of the force acting on the jet excavating units easy to carry out. Preferably, part of the support structure can be removed for the purpose of removing at least one of the jet excavating units. This is advantageous in particular in the event, for example, of maintenance to the excavating device or if the excavating device becomes jammed at an obstacle situated in front of one or more of the jet excavating units. Unlike in the known excavating device, the obstacle does not have to be displaced out of the path of the channel to be excavated or removed from ground level. The excavating device according to the invention simply has to be shut down and dismantled locally. The relatively small opening in the rear side of the excavating device which is caused by the local dismantling is small, so that the stability of the excavation front can be largely ensured. This leads to rapid, safe and effective removal of obstacles.
In another preferred embodiment, the support structure is provided with compartments which substantially completely surround the jet excavating units. This leads to a simple structure of the jet excavating units, and the support structure can assume certain functions of the jet excavating units.
In another preferred embodiment, one or more of the jet excavating units can be displaced with respect to the support structure, substantially parallel to the excavation direction, with the aid of a displacement device, in particular comprising a jack. It is thus possible for jet excavating units to be moved forwards in the excavation direction one by one or group by group with respect to the support structure and the other jet excavating units. In this case, in the first instance, the resistance presented by the soil to a single jet excavating unit or a group of jet excavating units is overcome as the jet excavating unit or units is/are moved forwards with their jet device(s) in operation, and then the resistance presented by the soil to another jet excavating unit, another group of jet excavating units and/or the support structure is overcome as it moves forwards. With a method of this type, a reduced propulsion capacity of the (drive device of the) excavating device and a reduced flow rate for the jet devices will be sufficient, since in this case the jet excavating units are not all moved forwards simultaneously in the excavation direction, and the jet devices are not all in operation simultaneously.
If the jet excavating units can be moved separately from one another, substantially parallel to the excavation direction, over a defined distance with respect to the support structure, obstacles in the ground can be at least partially dug out by allowing the jet excavating units situated outside the area of an obstacle to adopt an advanced position with respect to the support structure and allowing the jet excavating units which are situated inside the area of the obstacle to adopt a position which is as far back as possible with respect to the support structure, until further advance of the excavating device is impeded by the obstacle. Then, the obstacle, which has already been at least partially excavated around, is removed in the manner indicated above.
In a preferred embodiment, the at least one jet device of at least one jet excavating unit is adapted to expel a jet of jet liquid in a fixed direction. This measure means that the jet device does not comprise any moving parts and requires little maintenance, and little wear occurs.
In a further preferred embodiment, the jet of jet liquid which is expelled in a fixed direction from a jet device is oriented at an angle to the excavation direction, enabling the soil to be broken up and discharged effectively. In particular, the jet liquid jet expelled in a fixed direction from a jet device is inclined backwards as seen in the excavation direction and in the direction as the force of gravity (for a substantially horizontal excavation direction). This ensures that the soil is broken up and discharged effectively.
In another preferred embodiment, at least one of the jet excavation units comprises a number of jet devices, the jet liquid jets from which are oriented in different, fixed directions. This makes it possible to excavate the soil over the entire cross section of the jet excavating unit.
In this embodiment, it is possible in particular for the jet devices of a jet excavating unit to be operated intermittently, and more particularly alternately, each jet device covering, for example, an area of the cross section of the jet excavating unit. Similarly, the jet devices of different jet excavating units can be operated intermittently, and more particularly alternately. Tests have shown that jet excavation carried out intermittently does not reduce the effectiveness of the jet device compared to a jet device which expels a continuous flow of jet liquid. However, a substantial advantage of intermittent operation of jet devices is that the flow rate of jet liquid required, which can be supplied in a continuous flow and can be guided to different jet devices via controllable valves, is reduced considerably.
In another preferred embodiment, at least one of the jet devices is arranged on a side wall of the at least one jet excavating unit, the jet liquid jet expelled in a fixed direction from the at least one jet device being oriented substantially transversely to the excavation direction.
In a further preferred embodiment, the at least one jet device of an excavating unit comprises at least one tube which extends substantially in the excavation direction and is provided on its circumference with at least one outlet opening. In particular, the tube is arranged centrally in the jet excavating unit and the tube comprises a number of outlet openings which are positioned at a distance from one another as seen in the longitudinal direction of the tube and at different angles as seen in the circumferential direction of the tube. The jet device may comprise various tubes of this nature arranged centrally in the jet excavating unit or, to achieve the same results, may comprise a single tube which is internally divided into separate ducts by means of elongate partitions, with at least one outlet opening adjoining each of the separate ducts. If the outlet openings expel jet liquid jets which are such that each jet liquid jet covers part of the cross section, as seen from the front side of the jet excavating unit, and all the jet liquid jets together cover the entire cross section, the complete cross section of the soil entering the jet excavating unit is broken up. The shape of the three-dimensional cutting surface may be varied in such a manner that the cutting process is made as efficient as possible. The capacity of the outlet opening is selected according to the size of the cross-sectional part which is to be excavated by the outlet opening in question. By successively feeding a jet liquid jet to different tubes or ducts by means of controllable valves, an intermittent flow of jet liquid is produced at the at least one outlet opening connected to a tube or duct, and different parts of the cross section are successively covered by the jet excavating unit. By varying the order in which medium flows out of the various tubes or ducts, it is possible to adapt the efficiency of the excavation process.
Preferably, at least one jet excavating unit is provided with means in which the at least one jet device is releasably secured. This has the advantage that the jet device can easily be placed into and removed from the jet excavating unit, for example for maintenance purposes. For this purpose, the jet device preferably comprises a passage in a back wall of the jet excavating unit for introducing the jet device into the jet excavating unit, a closure means being provided for the purpose of bridging the pressure difference between the area in front of and behind the jet excavating unit when removing the jet device. It is then no longer necessary to even out the pressure in front of and behind the jet excavating unit before the jet device can be removed.
In the known excavating devices with bucket-wheel excavating devices, a probe which determines the nature of the soil in front of the excavating device cannot be used during the excavating process, but rather only when the excavating device is at a standstill. According to the prior art, the probe has to be removed before the excavating device is switched on. Therefore, continuous anticipation of the nature of the ground is not possible. Moreover, it is impossible to provide a continuous warning of obstacles. There is increased risk that obstacles will only be signalled after the excavating device has become stuck, which increases the levels of wear and may cause damage, in particular if the obstacle is an unexploded explosive object. By contrast, in a preferred embodiment the excavating device according to the invention has at least one probe which is adapted to determine the nature of the soil at a distance in front of the jet excavating units, as seen in the excavation direction, during excavation. This is a considerable advantage, since it enables the nature of the soil to be continuously anticipated. Another advantage is that the probe can be arranged at various locations in the cross section of the excavator shield and it is not restricted to a single location in the excavator shield, so that it is also possible to locally anticipate variations in the soil composition.
In a preferred embodiment, the excavating device comprises at least two probes for determining the nature of the soil between and around the at least two probes.
Preferably, there is at least one removable sealing means for sealing the space between adjacent jet excavating units or between a jet excavating unit and the support structure. As a result, it is possible for the jet excavating units to move independently of one another and to bridge the pressure difference which prevails between the area in front of and behind the jet excavating unit, where atmospheric pressure prevails.
Preferably, the at least one sensor connected to the at least one jet excavating unit is positioned between the support structure and the at least one jet excavating unit. This arrangement makes it easy to measure the forces acting on the jet excavating units, since the sensors can be fitted on the support structure.
The at least one sensor expediently comprises a piston-cylinder unit which can be operated by a fluid, which sensor is provided with pressure measuring means for recording a pressure of the fluid. The measured pressure is a measure of at least part of the force exerted on the sensor connected to the jet excavating unit or units. The piston-cylinder unit can also function as a displacement unit for displacing one or more jet excavating units of the excavating device substantially parallel to the excavating device with respect to the support structure.
In a preferred embodiment, the at least one jet excavating unit comprises at least one plate which is arranged substantially transversely to the excavation direction, the at least one sensor connected to the at least one jet excavating unit being adapted to measure substantially the force acting on the plate in the excavation direction. This has the advantage that the pressure being exerted by the soil is measured very directly.
In a preferred embodiment, the at least one sensor is connected, via the jet device, to the at least one plate, resulting in a functional unit which can be used in a jet excavating unit for jet excavation of the soil and measuring the force in the excavation direction at the location of the jet excavating unit.
In a preferred embodiment of the excavating device according to the invention, an excavation chamber is formed in a jet excavating unit by a space in which the at least one jet device is arranged, the excavation chamber being adjoined, on the rear side, as seen counter to the excavation direction, by, in succession, a front plate, which extends from the top side of the excavation chamber to a distance from the underside of the excavation chamber, and a back plate, which extends at a distance from the front plate, from the underside of the excavation chamber to a distance from the top side of the excavation chamber. The front plate and the back plate support the soil to be removed and allow controlled removal of the mixture of jet liquid and soil which is formed in the jet excavating unit. Furthermore, for this purpose a mixing chamber is formed behind the back plate, by a space with an outlet opening for discharging a mixture of soil and jet liquid. Preferably, a supply of mixing liquid, which may be the same as the jet liquid, is supplied to the mixing chamber via a feed, and the outlet opening is situated in the vicinity of an underside of the mixing chamber. The system line from the jet pump described above may lead to the mixing chambers of the jet excavating units.
The separation of the jet excavating unit into an excavation chamber and a mixing chamber makes it possible to set the flow rate of the jet liquid and the flow rate of the mixing liquid independently of one another. The flow rate of the jet liquid is determined by the resistance encountered from the soil and may vary considerably according to the soil conditions which occur. The flow rate of the mixing liquid for discharging the mixture of soil and jet liquid from the mixing chamber is determined by the minimum flow velocity which is required in order to entrain the soil particles multiplied by the cross section of the discharge line.
The front plate and the back plate separate the excavation chamber and the mixing chamber from one another. The front plate and the back plate preferably run substantially vertically (in the direction of the force of gravity). The (ratio of the) dimensions of the jet excavating unit are selected in such a manner that the incoming soil is initially forced to flow horizontally. Then, the soil is forced to flow upward, counter to the force of gravity, between the front plate and the back plate. The weight of the column of soil between the front plate and the back plate is sufficient to stabilize the excavation front by preventing soil from spontaneously flowing into the excavation chamber. The soil particles have to be actively stimulated to flow over the top edge of the back plate. The jet(s) in the excavation chamber cause a flow of water through the pores of the soil, in the direction of the opening between the front plate and the back plate. This flow of water ensures that a flow pressure is exerted on the soil particles, so that they start to float and friction between them is eliminated (fluidization), with the result that the mixture of soil and water which has been jet-excavated flows over the back plate. If the jets in the excavation chamber are shut down, the flow of soil from the excavation chamber to the mixing chamber stops immediately, with the result that the mixing chamber remains permanently open.
In a preferred embodiment, the mixing chamber comprises a space which is common to a number of jet excavating units, resulting in a simple and inexpensive structure.
To minimize the problems caused by obstacles which enter the mixing chamber via the excavation chamber, a crusher is arranged in the mixing chamber upstream of the outlet opening, which is able to crush the obstacles.
In a preferred embodiment, a non-return valve is arranged between the excavation chamber and the mixing chamber, in order to allow the mixture of soil and jet liquid to pass from the excavation chamber to the mixing chamber but blocking it from passing in the opposite direction. A mixture of soil and jet liquid is thus prevented from flowing back out of the mixing chamber into the excavation chamber if the pressure in the excavation chamber is too low.
Preferably, the front plate or the back plate is connected to a grate which extends from the underside or the top side of the excavation chamber to the front plate or back plate, respectively, in such a manner that material which is retained by the grate returns under the force of gravity to an area of the jet excavating unit which is reached directly by the liquid jet from the at least one jet device. The front plate and the back plate provide a desired flow of a mixture of soil and jet liquid which is situated in the jet excavating unit, while the grate prevents the discharge of the mixture becoming stagnant as a result of coarse material being retained.